Evaluate Performance Variables

Performance variables measure the success or failure of any human-computer interaction. Defining them for a particular setting is an essential initial step in the evaluation of outcomes. Common performance variables include:

	Basic Variables: Including functionality (what can the user do?), learning (how has performance improved?), time (how long to complete tasks?), errors (what, how often, and what consequences?), quality (how good is the output?), and robustness (how adaptable is the interaction?)
	Subjective Variables: Including acceptability (user rating) and enjoyability (was the interaction fun?)
	Condition Variables: Including fatigue (performance over time) and stress (performance under adverse conditions)
	Memory Variables: Including short-term load and long-term recall